The present invention concerns a structural improvement in supporting a detachable printing drum in a stencil printing machine.
Referring to FIG. 7, a general explanation will be made to a structure for supporting and guiding a detachable printing drum in a conventional stencil printing machine. The stencil printing machine is composed of functional units for such as perforating, printing, paper feeding, paper discharging, stencil discharging, image reading, and so on. Specifically, a perforating unit perforates a stencil sheet; a printing drum of a printing unit conducts printing with a perforated stencil sheet wrapped on the outer circumferential surface thereof. And a paper feeding unit provides paper with the printing drum; a paper discharge unit receives a printed paper. Further, a stencil discharge unit removes and discards a used stencil sheet from the printing drum. And an image reading unit reads an image from an original for perforation.
FIG. 7 illustrates the printing unit of the conventional stencil printing machine, specifically a structure for supporting and guiding the printing drum in the printing unit. In the drawing, reference numeral 2 indicates a forward side-plate; also reference numeral 4 indicates a rear side-plate. Reference numeral 6 indicates the printing drum, around which a perforated stencil sheet is wrapped, of the stencil printing machine. An ink supplying device is disposed inside the printing drum. An ink supplied by the ink supplying device is to be transferred to a printing paper through the printing drum and perforations formed in the stencil sheet.
Reference numeral 8 indicates a forward plate (a forward member); also reference number 10 indicates a rear plate (a rear member). Both the plates are connected with plural arms 12 to form a frame 13. In the frame 13, the printing drum 6 is rotatably supported around its axis between both the plates 8,10.
Reference numerals 14 and 16 indicate rail devices (sliding rails). Fixed rails 14a, 16a are supported horizontally between the two side-plates so as to be parallel to each other. In the rail devices, sliding rails 14b, 16b are respectively attached to the fixed rails 14a, 16a. The sliding rails 14b, 16b can move parallel with the fixed rails 14a, 16a. The sliding rails 14b, 16b can carry the frame 13. If the sliding rails 14b, 16b carrying the frame 13 move parallel with the fixed rails 14a, 16a, the printing drum 6 attached to the frame 13 moves between a printing position and a disengagement position. The printing position is inside the forward side-plate and the rear side-plate; and the disengagement position is outside the same (outside the machine).
A hook (not shown in the drawing) is disposed on the inner side of the sliding rails 14b, 16b for holding the arm 12 of the frame 13. By engaging the hook with the arm 12, the frame 13 is mounted on the sliding rails 14b, 16b. When the hook is engaged with the arm, the frame 13 can not move in the drum axial direction relative to the sliding rails 14b, 16b.
A supporting axis 20 for the printing drum 6 is extending through and protruding forward the forward plate 8. For convenience in illustration, the supporting axis 20 is drawn in imaginary line in FIG. 7. The printing drum 6 is rotatably supported on the frame 13 via the supporting axis 20. Further, a protruding portion 22 of a tube shape is fixed to a part of the forward plate 8, and the protruding portion 22 is parallel with the supporting axis 20. Holes 2a, 2b are formed in the forward side-plate 2. When the printing drum 6 is guided along the rail devices 14, 16 toward the printing position inside the machine, the supporting axis 20 is fitted into the hole 2a and the protruding portion 22 is fitted into the hole 2b. The protruding portion 22 is for detecting whether the printing drum 6 is in the position inside the machine; a detecting means is equipped with the outside of the forward side-plate 2, although it is not shown.
In the rear side-plate 4, there is formed a hole 4a through which the printing drum 6 is received into the inside of the machine. Two frame support members 18, 18 are disposed to the rear side-plate 4 to be respectively adjacent to the rail devices 14, 16. The frame support member 18 is in an approximate rectangular parallelopiped shape, and is fixed to the rear side-plate 4 with screws. The two frame support members 18, 18 have a protruding rib 18a respectively, which are formed on the inner sides thereof facing with each other. Further, engaging portions 11, 11 are integrally formed on the both sides of the rear plate 10. Each engaging portion 11 has a groove 11a formed in approximate U-shape.
By moving the frame 13 along the rail devices 14, 16 from the disengagement position outside the machine to the printing position inside the machine, each protruding rib 18a engages each groove 11a. As a result of the engagement, the frame support members 18 support the rear side of the frame 13 that carries the printing drum 6. Further, the forward side of the printing drum 6 is supported by engaging the supporting axis 20 with the hole 2a.
According to the conventional printing drum supporting device thus explained, the rear side (nearer side in FIG. 7) of the movable printing drum tends to be shaky, and printing matter obtained blurs in density in traverse direction thereof, which direction is parallel with the axial direction of the drum during stencil printing.
The object of the present invention is to provide a printing drum supporting device for a stencil printing machine, which is capable of overcoming the foregoing problems thus explained.